Teresias dum iret per silvam, vidit duos serpents coire, quos cum virga percussisset, in feminam mutatus est. Post octo annos dum videret eos similiter concumbentes et eos rursus percuteret, in pristinam restitutus est naturam.
--Vat. Myth. I.16
While Tiresias was wandering through the woods, he saw two snakes mating. When he struck them with a stick, he was changed into a woman. Eight years later, when he saw snakes mating in a similar fashion, he struck them again, and returned to his original shape (in pristinam naturam).